Kombu Kelp

Kombu kelp is a brown seaweed sold dried or as a fine powder. It is often used to make a Japanese soup stock called dashi.

In a study that surveyed seaweed samples from various Asian countries for their iodine content, it was found that kombu kelp contains, by far, the highest amount of iodine compared to other species of seaweed ().

Kombu kelp can contain up to 2,984 mcg of iodine per seaweed sheet (1 gram). This provides almost 2,000% of the recommended daily intake ().

Excess iodine consumption is well-tolerated in the majority of people but could result in thyroid dysfunction for those who are susceptible ().

Wakame

Wakame is another type of brown seaweed that is slightly sweet in flavor. It is commonly used to make miso soup.

The amount of iodine in wakame seaweed depends on where it is grown. Wakame from Asia has higher amounts of iodine than wakame from Australia and New Zealand ().

One study found that the average amount of iodine in wakame seaweed from various parts of the world was 66 mcg per gram, or 44% of the daily recommended intake ().

Nori

Nori is a type of red seaweed. Unlike brown seaweeds, it has a much lower content of iodine.

Nori is the type of seaweed that is commonly used in sushi rolls.

The iodine content in nori varies between 16–43 mcg per gram, or about 11–29% of the daily value (, ).

Summary Seaweed is an excellent source of iodine. However, the amount it contains depends on the species. Kombu kelp offers the highest amount of iodine, with some varieties containing nearly 2,000% of the daily value in one gram.

Dairy products are major sources of iodine, especially in American diets ().

The amount of iodine in milk and dairy differs greatly based on the iodine content in the cattle feed and the use of iodine-containing disinfectants during milking ().

A comprehensive study measured the iodine content in 18 different brands of milk sold in the Boston area. It found that all 18 brands had at least 88 mcg in 1 cup (8 ounces) of milk. Some brands even contained up to 168 mcg in one cup ().

Based on these results, 1 cup of milk can provide 59–112% of the recommended daily amount of iodine.

Yogurt is also a good dairy source of iodine. One cup of plain yogurt provides approximately half of the daily recommended amount ().

The amount of iodine in cheese varies depending on the type.

Cottage cheese is one of the best sources of iodine. One cup of cottage cheese provides 65 mcg, while one ounce of cheddar cheese provides about 12 mcg ().

Summary Although the exact amount of iodine in dairy products varies, milk, yogurt and cheese are major sources of it in the American diet.